双交联型泡沫凝胶的制备及其暂堵压井防漏机理

针对低压储层修井防漏技术难题，研发了一种双交联型泡沫凝胶压井液，基本配方为:3%聚丙烯酰胺+2%起泡剂+1.5%交联剂A+0.1%交联剂B。显微镜观察表明，单一交联型及双交联型泡沫凝胶均具有明显双膜结构，但双交联型泡沫凝胶膜更厚实，气核最外层凝胶膜厚度最大为77.35 μm，气核外层液膜总厚度最大为188.48 μm，表现为较好抗压强度和稳定性，其稳定时间大于10 d，远高于单一交联型体系。流变性与黏弹性测试表明，双交联型泡沫凝胶具有高弹低黏特征，利于泵送和后期返排解堵。暂堵压井模拟实验表明，对于渗透率在90～208 mD的中高渗岩心，在2 MPa正压差下60 min内作用于岩心的压降值≤ 0.05 MPa，滤失量几乎为零，该双交联型泡沫凝胶压井液具有一定抗压能力与低滤失特性，能有效暂堵储层，在低压油气井修井防漏领域具有较好应用前景。 

Development of a Double Crosslinked Foam Gel and its Mechanisms of Temporary Plugging,Well Killing and Mud Loss Controlling

When working over wells with low pressure reservoirs, loss of workover fluids into the reservoirs has long been a problem that needs to be resolved. A double crosslinked foam gel well killing fluid has been developed for the resolution of this problem. The basic composition of the killing fluid is:3% polyacrylamide + 2% foaming agent + 1.5% crosslinking agent A + 0.1% crosslinking agent B. It was found under microscope that single crosslinked foam gel and double crosslinked foam gel all had obvious dualmembrane structure, the double crosslinked foam gel had thick and tough membrane. The thickness of the membrane surrounding the gas core of the foam was 77.35 μm (max.) and the total thickness of the membranes surrounding the gas core was 188.48 μm (max.). The thick membranes render the foam gel high compressive strength and good stability. The foam gel can stay stable for at least 10 d, far longer than single crosslinked foam gel. Rheology and viscoelasticity test of the foam gel showed that the double crosslinked foam gel had high elasticity and low viscosity, making it easy to be pumped and flowed back. Simulated temporary plugging well killing experiments showed that for cores with porosity between 90 mD and 208 mD, pressure drawdown across the cores under 2 MPa positive pressure differential was less than 0.05 MPain 60 min, and the rate of filtration of fluid through the cores was almost zero. These data showed that the double crosslinked foam gel well killing fluid has a certain compressive capacity and low filtration rate, and can effectively plug reservoir rocks temporarily, rendering it good application prospects in preventing loss of workover fluids in low pressure reservoirs.